In these days, a so-called hybrid vehicle comprising an engine and an electric motor (electric motor generator) as power sources has been developed (refer to, for example, Japanese Unexamined Patent Application Publication No. 2000-224710). In the hybrid vehicle, an output shaft of the electric motor is coupled to an input shaft or an output shaft of a transmission. In the hybrid vehicle, the electric motor is used as the power source generating a driving torque for driving the vehicle together with the engine or by itself, or is used as a power source for starting the engine. Further, the electric motor is used as an electric motor generator for generating a regeneration torque to provide a breaking force to the vehicle, or is used as an electric motor generator for generating an electric power which is supplied to and stored in a battery of the vehicle. These usages of the electric motor can improve a total energy efficiency (fuel consumption) of the vehicle as a whole.